The only free and comprehensive online etymological dictionary of the Spanish language
alma f. (Noun) "soul"
11th cent. From Latin anima "breath," "soul." From Proto-Italic *anamo- 'id.' From Proto-Indo-European *h2enh1-mo- "breath." From the root *h2enh1- "to breathe" and the noun-forming suffix *-mó- (see -mo).
Indo-European
Romance
Asturian alma, Portuguese alma, Galician alma, Catalan ànima, Occitan anma, French âme, Italian alma, Dalmatian jamna, Aromanian inimã, Romanian inimă, Sardinian àmina
Italic
Oscan anams
Celtic
Old Irish anim, Middle Breton eneff, Cornish enef
Hellenic
Ancient Greek ἄνεμος (ánemos) "wind," Mycenaean a-ne-mo- "winds"
Basque
Basque arima (< Vulgar Latin *alima)

An expected development from Latin would be Latin anima > Vulgar Latin *anma > Spanish alma through a normal syncopation of the middle -i-, as advocated by Rini (1999). However, a clue may survive in Basque arima, which is probably a loanword from Vulgar Latin. Dissimilation must have occured before syncopation of the middle vowel, which is more likely from *alima than by direct dissimilation from anima (Trask 2008). Therefore, *alima may have briefly existed in Iberia before swiftly syncopating to *alma.