The Way of the Word

I. It turns out that "interesting" was quite recently a euphemism for pregnant; see these OED examples:

1930 GALSWORTHY On Forsyte 'Change 171 Winifred, beginning to be ‘interesting’, owing to the approach of a little Dartie, kept her eyes somewhat watchfully on ‘Monty’. 1970 K. GILES Death in Church ii. 49 Her little maid got into An Interesting Condition and the young fellow was willing to solemnise it.

II. Here's a famous passage from Congreve's play The Way of the World (1700) about interest and pregnancy. The situation should be fairly self-explanatory: Mirabell and Mrs Fainall were [and are probably still] lovers, and he married her off to a friend of his to shield her potentially "interesting condition." (Fainall was induced to marry her for her money.)

MRS. FAINALL
While I only hated my husband, I could bear to see him; but since I have despised him, he's too offensive.

MIRABELL
Oh, you should hate with prudence.

MRS. FAINALL
Yes, for I have loved with indiscretion.

MIRABELL
You should have just so much disgust for your husband as may be sufficient to make you relish your lover.

MRS. FAINALL
You have been the cause that I have loved without bounds, and would you set limits to that aversion of which you have been the occasion? Why did you make me marry this man?

MIRABELL
Why do we daily commit disagreeable and dangerous actions? To save that idol, reputation. If the familiarities of our loves had produced that consequence of which you were apprehensive, where could you have fixed a father's name with credit but on a husband? I knew Fainall to be a man lavish of his morals, an interested and professing friend, a false and a designing lover, yet one whose wit and outward fair behaviour have gained a reputation with the town, enough to make that woman stand excused who has suffered herself to be won by his addresses. A better man ought not to have been sacrificed to the occasion; a worse had not answered to the purpose. When you are weary of him you know your remedy.

III. The converse, of course, is true to a degree -- conception, abortion, pregnant, embryonic, fertile, and miscarriage are all potentially applicable to thoughts and actions. This paradigm does, however, lead to odd results if you substitute synonyms: e.g. a knocked-up pause, an absolutely third-trimester notion, a phrase gastrulating with meaning, a fetal vagueness, an amniotic fluidity.