http://www.moonfleetonline.co.uk/history/illegitimacy/

'How illegitimacy was recorded

PARISH REGISTERS
There are a number of latin words used to denote illegitimacy

ignotus = unknown (ie father unknown)
spurius = spurious
filius populi = son of the people, this is usually used where the father was a local lad but could be one of several
filius nullius = son of none, usually used where the father was a stranger or the girl would not give any information about him
There are also a number of English words used in parish registers to convey illegitimacy, base, bastard, spurious, imputed, misbegotten, chance begotten.

Sometimes a child would be described in the baptism register as

Baptised William son of Sarah Smith and the reputed son of William Brown.'