prefix, suffix
cheap; low-priced
Prefix or suffix used in compounds to indicate something is inexpensive or of low cost. Often seen in words like 安売り (bargain sale) or 格安 (bargain-priced).
この店は安売りをよくやっている。
This store often has bargain sales.
格安の航空券を見つけた。
I found a bargain-priced plane ticket.
prefix
Prefix used in compounds to indicate a lack of careful consideration, often implying a hasty or frivolous action. Common in words like 安請け合い (rash promise) or 安易 (easy-going, thoughtless).
See also: 安請け合い
彼は安請け合いをして後悔した。
He made a rash promise and regretted it.
安易な考えで行動
You shouldn't act on thoughtless ideas.
安い is the standalone adjective meaning 'cheap', while 安 is a bound morpheme used in compounds.
安易 means 'easy-going' or 'thoughtless' as a standalone word, whereas 安 in this sense only appears as a prefix in compounds.
The kanji 安 carries meanings of 'peaceful', 'cheap', and 'easy'. The reading やす is a native Japanese reading (kun'yomi) used in compounds. The exact historical derivation of the prefix/suffix usage is uncertain, but it likely developed from the adjective 安い (cheap) and related concepts of ease or lack of restraint.