The English adjective pregnant has several meanings: carrying a fetus or fetuses within the womb, full of meaning or significance, inventive or imaginative, prolific or fruitful.
It is from the Latin adjective praegnans/praegnant-, with child, pregnant, variant of praegnas/praegnat-, probably from the prefix prae-, before, and the stem of the verb gnasci (past participle gnatus), to be born.
The French adjective prégnant(e) is mainly used to mean full of meaning or significance, and the equivalent of the English adjective pregnant in the sense having a child developing in the uterus is the feminine adjective enceinte, from Latin inciens/-tis, of same meaning.
This Latin word is related to Greek ἔγκυος (= egkuos), swelling inside, i.e. big with child, from the preposition ἐν (= en), meaning inside, and the verb κύω (= kuó), to swell, to be pregnant. From this verb, the noun κῦμα (= kuma) meant a wave, surge, billow.
It has often been said that the adjective enceinte is from incincta, the feminine past participle of the verb incingere, meaning to gird, surround, from the prefix in-, meaning in, and cingere, to gird. Conversely, in his etymological encyclopedia, Etymologiae, the Spanish archbishop and Doctor of the Church St Isidore of Seville (circa 560-636) explained the word as in-cincta, ungirt, from the privative prefix in- and cincta, past participle of cingere,
because the enlarged womb does not permit a pregnant woman to be tightly girt.
These erroneous etymologies might reveal a reluctance to allude to a ‘swollen’ woman. Indeed, in French, the adjective enceinte only applies to women: to refer to a pregnant animal, the French word is grosse, feminine of gros, in the sense swollen.
However, the standard word for a woman’s pregnancy is une grossesse. And the vulgar verb engrosser, literally to make (a woman) ‘grosse’, is the equivalent of to knock (a woman) up. In the popular idiom être en cloque (which corresponds to the standard expression être enceinte, to be pregnant), cloque means hump.
The same image is found in another popular expression, avoir un polichinelle dans le tiroir/sous le tablier, literally to have a Punchinello in the drawer/under the apron.