paulus.

From earlier paullus, likely from Proto-Italic *paukslos, from Proto-Indo-European *peh₂w- (“few, small”) + *-ko- + *-slom, the first two elements also giving Latin paucus (“few”). Details Cf. the proportions paullus :: paucus like axis :: āla like veicus :: veilla, and with diminutives paullus :: pauxillus like āla :: āxilla like aulla :: auxilla. veilla and aulla showcase the same development of /diphthong + ks/ as the present word. māla, vēlum, pālus are further examples of words formed with the same suffixes. Against this, De Vaan (2008) notes that "the suffix *-slo- is otherwise only used for instrument nouns, and only after consonant stems; both are reasons to reject a preform *pauk-slo- derived from *pau-ko-", and quotes Thurneysen (1907: 177) as deriving it from Proto-Italic *paurelos, from Proto-Indo-European *péh₂uros, also from *peh₂w-. However, the regular development of the cluster /wr/ is metathesis, as in parvus, and just this is attested in parvulus. It's difficult to envision a split outcome of metathesis for the base form and its morphologically transparent diminutive (cf. the systematic parallels above). The "instrument nouns" objection can be countered with the striking parallel in pullus (“animal young”) :: pusillus (“tiny”) and by the cross-linguistic tendency to refer to the young with neuter or otherwise objectifying nouns (cf. German -chen); the precise meaning of the suffix also need not have been an instrument. Further related to Latin pauper, puer, Ancient Greek παῦρος (paûros), English few.