What is the meaning of -tu?

Form of -ytu used after nouns ending in consonants.

A verb-forming suffix.

Used to form adjectives, roughly corresponding to the English past participle forming suffix -ed.

-less

alternative form of -ttu

postpositive form of te

nominalizing suffix deriving agent nouns of feminine gender (see -ti for masculine).

Nominalizes verbs to indicate the agent of an action: -er

-ness, -ity

enclitic form of þú

ablative singular of -tus

Form of -tı after the vowels O / U.

Source: wiktionary.org