Lactante e lactente

Lactante (nursing mother) and lactente (suckling, baby) are two interesting Portuguese words. Lactante comes from Latin lactans, lactantis, present participle of lacto, lactare, to breast-feed; lactente, from Latin lactens, lactentis, present participle of lacteo, lactere (to suckle). Both are ultimately derived from Latin lac, lactis, milk, which became leite in Portuguese, leche in Spanish, lapte in Romanian, latte in Italian, lait in French and llet in Catalan. The stem lact can be found, for instance, in English lactate, to secrete milk and its derivative lactation, in lactic, of or relating to milk, and lactose, sugar present in milk, among others. Something else that is worthy of mention is that Latin lac, lactis, a neuter word, became masculine in Portuguese, Italian and French, feminine in Spanish and Catalan and remained neuter in Romanian.

However, all of this is not why I started this topic. The pair lactare lactere is probably the only case among Latin verbs of a causative verb built by changing the theme vowel (in this case from a to e). This reminds me of what happens in Japanese with a few verbs, one having an active meaning and the other a passive one, as in 過ごす(sugosu, to spend) and 過ぎる (sugiru, to pass); 落とす(otosu, to drop) and 落ちる (ochiru, to fall); 乾かす(kawakasu, to dry - trans.) and 乾く(kawaku, to dry - intr.) , and in English to fall vs. to fell, to rise vs. to raise and to lie vs. to lay.

Our sister language Spanish doesn't make this useful distinction regarding lactante and lactente and only knows the the former, which means both nursing mother and suckling.