Piecemeal is (1) an adjective meaning done piece by piece, (2) an adverb meaning little by little, and (3) a noun denoting something done piecemeal or a piecemeal way of doing something.
Piecemeal works as an adverb, so adverbial phrases such as in a piecemeal manner and in a piecemeal fashion can usually give way to just piecemeal, with no helper words. For example, “we wrote the report in a piecemeal manner” can become “we wrote the report piecemeal.” Piecemeal is an unusual adverb, though, as it is postpositive, meaning it follows what it modifies. “We piecemeal wrote the report” sounds wrong, while synonymous adverbs could fit in that slot with no problem (e.g., “we gradually wrote the report” sounds fine).
The modern spelling of the word has no hyphen. Peacemeal is a misspelling.
The word developed around 1300.1 Piece meant what it means now, and the suffix -meal meant by, where by bears the same sense as in phrases such as piece by piece and bit by bit.2 The word took several spellings over the years before the modern spelling was settled in the 19th century.3
The rest of their large possessions had been torn piecemeal from their grasp, and Granada, the city of their love and pride, alone remained. [The Penny Magazine (1835)]
When we see an eager assailant of one of these wrongs, a special reformer, we feel like asking him, What right have you, sir, to your one virtue? Is virtue piecemeal? ["New England Reformers," Ralph Waldo Emerson (1844)]
The frost and the tempests of unnumbered ages had battered and hacked at these cliffs, with a deathless energy, destroying them piecemeal. [A Tramp Abroad, Mark Twain (1880)]
Data has been uncovered relating that the planes were smuggled in piecemeal through North Sea ports, and then assembled. [Reading Eagle (1934)]
Television’s new season will probably get off to a piecemeal start this fall because of the recent four-month writers’ strike. [Williamson Daily News (1973)]
Each victim’s family would receive $10m, but the money would only be handed over piecemeal, as sanctions on Libya were lifted. [BBC]
Free trade agreements are now procured piecemeal rather than in toto, regionally rather than globally. [The Australian (2012)]