Alastair \a-las-tair, al(a)-stair\ as a boy's name (also used as girl's name Alastair), is of Greek origin, and the meaning of Alastair is "man's defender". Scottish variant of Alistair, from Alexander. Most of the variants are different phonetic spellings of the name. TV commentator Alistair Cooke; actor Alistair Sim.

Alastair has 26 variant forms: Al, Alasdair, Alasteir, Alaster, Alastor, Alaisdair, Alaistair, Alaister, Aleister, Alester, Alistair, Alistar, Alister, Allaistar, Allaster, Allastir, Allistair, Allister, Allistir, Allysdair, Allystair, Allyster, Alysdair, Alysdare, Alystair and Alyster.

Baby names that sound like Alastair are Alistir, Alistaire and Alisdair.