mast-

1.
variant of masto- before a vowel:
mastectomy.
British Dictionary definitions for mast-

mast-

combining form
1.
a variant of masto-

masto-

combining form
1.
indicating the breast, mammary glands, or something resembling a breast or nipple: mastodon, mastoid
Word Origin
from Greek mastos breast
mast- in Medicine

mast- pref.
Variant of masto-.