What does fastly mean?
'Fastly' is an archaic English adverb that once meant 'quickly' or 'swiftly', and in still earlier usage 'firmly' or 'securely'. Although it follows the familiar pattern of forming adverbs with '-ly', it dropped out of standard English long ago, leaving the plain word 'fast' to serve as both adjective and adverb — one of the few cases in modern English where the adverb lacks the expected '-ly' ending. Because of this gap, 'fastly' strikes many learners as a natural word, yet using it today would be considered nonstandard. Its history is instructive: the root 'fast' originally conveyed the idea of being firmly fixed or held, as in 'steadfast' and 'hold fast', and only later came to signify speed. 'Fastly' preserves a trace of that transition, surviving now mainly in historical literature and serving as a reminder that even seemingly obvious word forms can fall out of use.
adverb (archaic)An archaic adverb meaning 'quickly, swiftly', and in older use also 'firmly, securely'. It is no longer part of standard modern English, where the adverb is simply 'fast'.
- (archaic) Quickly, rapidly, with great speed.
- (archaic) Firmly, securely, tightly — reflecting the older core sense of 'fast' as fixed or rooted rather than speedy.
"The messenger rode fastly to deliver the king's decree before nightfall."
"She ran fastly through the crowded market, dodging vendors and carts."
"The door was shut fastly against the winter wind."
It sounds perfectly normal, but 'fastly' vanished from English centuries ago — the correct adverb today is simply 'fast'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fastly
'Fastly' derives from Old English 'fæste', the adverbial form of 'fæst', meaning firm, fixed, or secure — the same root behind 'steadfast' and 'hold fast'. In Middle and Early Modern English, 'fastly' could mean both 'firmly' and 'quickly', since 'fast' had acquired its speed sense by way of the idea of moving with firm, vigorous intensity. As 'fast' alone became the standard adverb, 'fastly' faded into obsolescence. Its cognates include German 'fest' (firm) and related Germanic forms sharing the same ancient root.
How fastly is actually used
'Fastly' is obsolete in modern standard English and will strike most readers as an error, even though it feels intuitive because adverbs typically take '-ly'. In contemporary writing, always use 'fast' instead ('he runs fast'). The word survives only in historical texts, and its older sense of 'firmly' shows how 'fast' originally meant fixed or secure before its speed sense became dominant.
Easily confused with fastly
'Fast' is the standard modern English adverb for quick movement, whereas 'fastly' is an archaic form that sounds natural to many speakers but is not accepted in current standard usage.