мелче

By surface analysis, *melь (*melʹ) +‎ -че (-če, diminutive suffix). Related to Romanian melc (“snail”), with no direct cognates in other Slavic languages:

• Mladenov: Akin to Proto-Slavic *(s)mъlžь (“mollusc”).
• Georgiev (БЕР): Semantically parallel to dial. пасоче (pasoče) < па- (pa-) +‎ сок (sok, “juice”) +‎ -е (-e), слимак (slimak) < Proto-Slavic *slima (“slime”) +‎ -ак (-ak).
• Duvernois: Borrowed from Romanian or together with the Romanian lemma - inherited from a Paleo-Balkan substrate.

In either case, probably ultimately from Proto-Indo-European *(s)mel- (“meek, tender, soft”) (attested e.g. in Old Armenian մեղկ (mełk, “soft”)).

• IPA^(key):

ме́лче • (mélče) n (dialectal)

1. river snail (grastropod from family Viviparidae)
2. (figurative) timid, meek, unassertive person or creature

• ме́лчо m (mélčo) (in the figurative sense only)

• Georgiev, Vladimir I., editor (1986), “мелче”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volume 3 (крес¹ – мѝнго¹), Sofia: Bulgarian Academy of Sciences Pubg. House, page 729
• Nayden Gerov (1899) “ме́лчё”, in Рѣчникъ на Блъгарскꙑй язꙑкъ. Съ тлъкувание рѣчи-тꙑ на Блъгарскꙑ и на Русскꙑ. [Dictionary of the Bulgarian language]‎ (in Bulgarian), volume 3, Plovdiv: Дружествена печꙗтница "Съгласие.", page 59