Other forms: altered, altering, alters
To alter something is to change part of it and leave the rest standing. You alter a plan rather than scrap it: move the meeting an hour later, take an inch off the trousers, repaint one wall.
Alter is the tidier, more official cousin of change, so it lives in contracts, notices and instructions — the timetable has been altered, we reserve the right to alter these terms. In sewing it is close to a technical word: a shop that alters clothes takes them in, lets them out, shortens a hem, and the job itself is an alteration. Things alter by themselves too: his face altered when he heard the news. The noun alteration nearly always means a small fix, not a rebuild. And watch the spelling — an altar is the table at the front of a church, and it is a different word.
1verbalterTo change part of something, or to change it in a small way.
“They altered the design after the first round of tests.”
formal in this meaning — an editor’s judgement
2verbbecomeTo become different.
“Her expression altered the moment she saw who was waiting.”
formal in this meaning — an editor’s judgement
synonyms: change
3verbclothingTo change a piece of clothing so that it fits properly.
“She had the dress altered across the shoulders before the wedding.”
Also accepted in games: modify
Alter came through Old French alterer from Medieval Latin alterō, to make other, and behind that sits Latin alter, the other. The same al- runs through alias and alien — another name, another country. To alter a thing is to make it other than it was, but only a little, or it would stop being the same thing at all.
Proto-Indo-European
*h₂el- (other)
Latin
alter — the other
Medieval Latin
alterō — to make other
Old French
alterer
English, today
alter
Built from
From Old French alterer (French altérer), from Medieval Latin alterō (“to make other”), from Latin alter (“the other”), from al- (seen in alius (“other”), alienus (“of another”), etc.; see alias, alien, etc.) + compar. suffix -ter.
Etymology from Wiktionary, CC BY-SA