Latvian proper noun Jelgava and 17th century countable noun jelgava (“town, city”) (later replaced by pilsēta) are popularly believed to be a borrowing from Livonian jālgab (“town, city”). Karulis, however, thinks that this word doesn't have a plausible Finnic etymology and suggests it being a borrowing from Latvian, in Latvian ultimately from *Heh₃l- (“to bend”) whence also leja (“underside, depression, valley”), dialectal meanings of elks (“elbow, part of sleeve around elbow, turn, angle”), elkonis (“elbow”). The name of Jelgava could also be related to dialectal jelgs (“wet”) or the noun jelga (“a swampy place”).[1]
Karulis' version, however, raises questions as Jelgava has been historically called Mītava and Mitau in Latvian and German respectively (according to Karulis himself of Baltic stock, cognate with the verb mīt (“to stagger, shift, trade”)). (Kersti Boiko also tangentially mentions Nītauja as an earlier name for Jelgava.) Suggesting Livonian borrowing from Latvian a term that perhaps was not even used in Latvian at that time is anachronistic.
Jālgab
LĒL gives type 156 for this word. This type in singular is identical to type 157 but has vowel shift in plural, since Jālgab is an uncountable proper noun such plural vowel shift is unknowable and perhaps this is an error, thus type 157 is indicated in this entry.
The countable noun version jālgab has type 159 indicated which too is almost identical to type 157 except for short locatives (a common variation), the declension table in this entry gives both short and long locatives.