In Hebrew the "lamb" is SEH (sheen-hey), and it happens to be in MASCULINE form with MASCULINE verbs. Therefore, the "lamb" IS a "ram", rendered from AYIL (alap-yodh-lamed).
Now here is where it gets interesting. When the male lamb is just part of the flock it is called SEH, but when it is set apart for sacrifice (as a male lamb) it then "graduates" to the word AYIL. Thus, once the ram was designated after being caught in the thicket, he went from SEH to AYIL.
Hebrew Word: Lya
Transliterated Word: 'ayil
Ge 15:9 And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon.
Ge 22:13 And Abraham lifted up his eyes, and looked, and behold behind him a ram caught in a thicket by his horns: and Abraham went and took the ram, and offered him up for a burnt offering in the stead of his son.
Ge 31:38 This twenty years have I been with thee; thy ewes and thy she goats have not cast their young, and the rams of thy flock have I not eaten.
Ge 32:14 Two hundred she goats, and twenty he goats, two hundred ewes, and twenty rams,
If that doesn't make sense to you, then we also have to remember that God Himself never said on that particular day He would provide anything whatsoever, let alone a lamb. Abraham and Isaac said it! Abraham trusted YHWH to provide a sacrifice, which is we need to focus on.
While we're on the subject of sin sacrifices, we also must remember that YHWH was merciful enough to accept not just lambs or bulls, but various kinds of sin sacrifices, depending on what the person could afford (i.e, Leviticus 5:7 and 11; Leviticus 12:8; Leviticus 14:22 and 30).