Other forms: bastards
In its oldest sense a bastard is a child born to parents who were not married, a fact that mattered enormously in law and inheritance for centuries and appears constantly in history and older fiction.
In modern speech it is almost always an insult aimed at a man — or, confusingly, an affectionate one between friends, where lucky bastard is close to praise. It is coarse either way. It also attaches to difficult things rather than people: a bastard of a job. Recognise it; think twice before using it.
1nouninsultA rude word for a man you dislike — or, said warmly, for one you like.
“The lucky bastard won it twice.”
2nounbastardA child born to parents who are not married.
“In those days a bastard could inherit nothing.”
Too few real examples of this word to estimate which sense is commonest.
The old explanation lives in the phrase fils de bast, a packsaddle son, got on the road rather than in a marriage bed. Old French bastart meant an illegitimate child, and the insult came afterwards.
Middle English
bastard
English, today
bastard
Built from
From Middle English bastard. From Middle English bastard, bastarde, from Old English bastard, from Anglo-Norman bastard, Old French bastart (“illegitimate child”), perhaps via Medieval Latin bastardus, of unknown origin. Likely from Frankish bāst (“marriage, relationship”) + -ard, -art. Frankish bāst derives from a North Sea Germanic variety of Proto-Germanic banstuz (“bond, connection, relationship, marriage with a second woman of lower status”), from Proto-Indo-European bʰendʰ- (“to tie, bind”) and is related to West Frisian boaste (“marriage, matrimony”), Middle Dutch bast (“lust, heat”), and more distantly to English boose* (“cow-stall”). The term probably originally referred to a child from a polygynous marriage of heathen Germanic custom — a practice not sanctioned by the Christian churches.
Etymology from Wiktionary, CC BY-SA