LIV (following Vendryes)[1] and KPV[2] assign this to Proto-Indo-European*delǵʰ-(“to become firm”). Matasović says that *dl̥h₁gʰós should not be connected here and assigns no etymology, but also compares Albanianndal(“to stop”).[3]
This verb had two present stems attested in Celtic: *delgeti and the *-sḱéti present *dalsketi. Here is the conjugation with *delg-e/o- as the present stem:
Thematic present, suffixless preterite
Active voice
Present
Imperfect
Future
Preterite
1st singular
*delgū
*delgemam
*didlixsū
*dalga
2nd singular
*delgesi
*delgetās
*didlixsesi
*dalgas?
3rd singular
*delgeti
*delgeto
*didlixseti
*dalge
1st plural
*delgomosi
*delgemo
*didlixsomosi
*dalgmo
2nd plural
*delgetesi
*delgestē
*didlixsetesi
*dalxte
3rd plural
*delgonti
*delgento
*didlixsonti
*dalgars
Pres. subjunctive
Past subjunctive
Imperative
1st singular
*delxsū
?
—
2nd singular
*delxsesi
?
*delge
3rd singular
*delxseti
?
*delgetou
1st plural
*delxsomosi
?
*delgomos
2nd plural
*delxsetesi
?
*delgete
3rd plural
*delxsonti
?
*delgontou
Passive voice
Present
Imperfect
Future
Preterite
1st singular
*delgūr
—
*didlixsūr
*dalgra
2nd singular
*delgetar
—
*didlixsetar
*dalgras?
3rd singular
*delgetor
?
*didlixsetor
*dalgre
1st plural
*delgommor
—
*didlixsommor
?
2nd plural
*delgedwe
—
*didlixsedwe
?
3rd plural
*delgontor
?
*didlixsontor
?
Pres. subjunctive
Past subjunctive
Imperative
1st singular
*delxsūr
—
—
2nd singular
*delxsetar
—
—
3rd singular
*delxsetor
—
—
1st plural
*delxsommor
—
—
2nd plural
*delxsedwe
—
—
3rd plural
*delxsontor
—
—
Declension of the present participle
masculine
singular
dual
plural
nominative
*delgonts
*delgonte
*delgontes
vocative
*delgonts
*delgonte
*delgontes
accusative
*delgontam
*delgonte
*delgontans
genitive
*delgantos
*?
*delgantom
dative
*delgantei
*delgantbom
*delgantbos
instrumental
*delgantī?
*delgantbim
*delgantbis
feminine
singular
dual
plural
nominative
*delgantī
*delgantī
*delgantiyās
vocative
*delgantī
*delgantī
*delgantiyās
accusative
*delgantīm
*delgantī
*delgantiyans
genitive
*delgantyās
*?
*delgantyom
dative
*delgantyāi
*delgantyābom
*delgantyābos
instrumental
*?
*delgantyābim
*delgantyābis
neuter
singular
dual
plural
nominative
*delgont
*?
*delgonta
vocative
*delgont
*?
*delgonta
accusative
*delgont
*?
*delgonta
genitive
*delgantos
*?
*delgantom
dative
*delgantei
*?
*delgantbos
instrumental
*delgantī?
*?
*delgantbis
Declension of the middle participle
masculine
singular
dual
plural
nominative
*delgomnos
*delgomnou
*delgomnoi
vocative
*delgomne
*delgomnou
*delgomnoi
accusative
*delgomnom
*delgomnou
*delgomnons
genitive
*delgomnī
*delgomnous
*delgomnom
dative
*delgomnūi
*delgomnobom
*delgomnobos
instrumental
*delgomnū
*delgomnobim
*delgomnobis
feminine
singular
dual
plural
nominative
*delgomnā
*delgomnai
*delgomnās
vocative
*delgomnā
*delgomnai
*delgomnās
accusative
*delgomnam
*delgomnai
*delgomnans
genitive
*delgomnās
*delgomnous
*delgomnom
dative
*delgomnai
*delgomnābom
*delgomnābos
instrumental
*?
*delgomnābim
*delgomnābis
neuter
singular
dual
plural
nominative
*delgomnom
*delgomnou
*delgomnā
vocative
*delgomnom
*delgomnou
*delgomnā
accusative
*delgomnom
*delgomnou
*delgomnā
genitive
*delgomnī
*delgomnous
*delgomnom
dative
*delgomnūi
*delgomnobom
*delgomnobos
instrumental
*delgomnū
*delgomnobim
*delgomnobis
Declension of the past participle
masculine
singular
dual
plural
nominative
*dlixtos
*dlixtou
*dlixtoi
vocative
*dlixte
*dlixtou
*dlixtoi
accusative
*dlixtom
*dlixtou
*dlixtons
genitive
*dlixtī
*dlixtous
*dlixtom
dative
*dlixtūi
*dlixtobom
*dlixtobos
instrumental
*dlixtū
*dlixtobim
*dlixtobis
feminine
singular
dual
plural
nominative
*dlixtā
*dlixtai
*dlixtās
vocative
*dlixtā
*dlixtai
*dlixtās
accusative
*dlixtam
*dlixtai
*dlixtans
genitive
*dlixtās
*dlixtous
*dlixtom
dative
*dlixtai
*dlixtābom
*dlixtābos
instrumental
*?
*dlixtābim
*dlixtābis
neuter
singular
dual
plural
nominative
*dlixtom
*dlixtou
*dlixtā
vocative
*dlixtom
*dlixtou
*dlixtā
accusative
*dlixtom
*dlixtou
*dlixtā
genitive
*dlixtī
*dlixtous
*dlixtom
dative
*dlixtūi
*dlixtobom
*dlixtobos
instrumental
*dlixtū
*dlixtobim
*dlixtobis
The alternative present stem *dalsketi conjugates as follows:
In Brittonic, the vowel of *dalsketi somehow hybridized with the consonantism of *delgeti to form *dalgeti. Schumacher thinks this influence spread from the preterite stem *dalg-.[2]
↑ 2.02.1Schumacher, Stefan, Schulze-Thulin, Britta (2004) Die keltischen Primärverben: ein vergleichendes, etymologisches und morphologisches Lexikon [The Celtic Primary Verbs: A comparative, etymological and morphological lexicon] (Innsbrucker Beiträge zur Sprachwissenschaft; 110) (in German), Innsbruck: Institut für Sprachen und Literaturen der Universität Innsbruck, →ISBN, pages 271-273