Alter and Altar are easily confused words. The spell-check of most word processing software programs would not catch a slip-up among these three words. As long as it’s a word and it is spelled correctly, spell-check keeps on scanning the document.
Alter is a verb. It means to change the appearance or the composition of an object’s design. Clothes are altered when pants legs or dress hems are shortened, or waist lines are tucked in.
Altar is a noun. It means a central table where religious rituals are performed within a church or other ceremonial space.
The following sentence uses both words correctly:
Every Saint’s feast meant altering the entire sanctuary’s decorations, from the altar to the walls. Alistair, the new vicar, shook his head in disbelief at all this pageantry and fuss.