Dia dhaoibh a chairde,
I am interested in all the Irish words denoting hills and mountains and especially how they might relate to their physical characteristics. Here's how I'm doing so far

BEANN- Mountain with a pointed top,sharp ascent
MULLACH- Mountain with a broad flattish shoulder before the top
CRUACH-Rounded Hill
SLIABH/CNOC/ARD Hill
TULLACK-Smaller Hill
DROIM-Ridge

Slan
Elaine

"Mullach" doesn't denote a type of hill as such.It just means "summit"
"Sliabh" means specifically "mountain", not "hill"
And the word is spelt "Tulach".
Otherwise you seem fine.

Tá an ceart ag an Laighneach ach tá an sampla seo ag Dinín: mullach socair, a level top or summit. Also, for Elaine's benefit, here are a couple samples from the Dinneen Dictionary combining two terms each from your list above in common expressions: mullach sléibhe, a mountain top; mullach an chnoic, the summit of the hill. Mullach also has a common diminutive form, mullóg. (In fact, there are various variants of the words on your list, mostly minor and mostly diminutives.)

Here are two new ones for you:

com (masc.) -- coomb, cirque, mountain recess (so it's a hollow or depression up on a hill or mountain)
mám (masc.) -- mountain pass

Both show up in placenames.

Seanfhocal: Is glas na cnoic i bhfad uainn. Faraway hills are green.

And this curiosity: Cnoc ort. Bad luck to you. (Or 'Woe be thine' as only Dinneen could put it.) Literally, the prase means 'a hill on you'. Because a hill would be a heavy burden? Or that you might have to take to the hills? There are some expressions in this latter vein having to do with the days of oppression our ancestors endured.