Do you have any examples of nouns that are formed by adding -al to a verb? I can think of one example (rental), but would like to have a few more. Thank you for your help!
There are a fair number of deverbal nouns ending in -al: examples include arrival, disposal, dismissal, denial, betrothal, approval, appraisal, avowal, betrayal, trial. You can find more examples by looking through the results of this search on the dictionary aggregator site OneLook for nouns ending in
The Wiktionary entry on the suffix -al points out that in some cases, -al nouns coexist with -tion or -sion nouns from the same verb, as with proposal and proposition.
Describing the verbs that take -al as a suffix
A number of linguists have been interested in figuring out rules about which verbs take -al as a noun-forming suffix. It has been observed that the noun-forming suffix -al only attaches to verbs that are stressed on the final syllable. There are some more complicated conditions that have been hypothesized to apply to the use of this suffix; you can see some discussion in "Against Phonological Conditioning of WFRs", 1992, by Anna Malicka-Kleparska, or in "Phonotactic Properties of Morphological Units", by Edmund Gussmann and Bogdan Szymanek, in Morphologie: Ein Internationales Handbuch Zur Flexion und Wortbildung, Volume 1.
Malicka-Kleparska, citing Marchand 1969:237, says that trial and rental ought to be regarded as loaned words, rather than as words that have been formed in accordance with the English derivational system. These two words do not conform to a generalization that says that -al attaches only to Latinate verbs with the structure prefix + root (p. 435 in Phonological Investigations, edited by Jacek Fisiak and Stanislaw Puppel). According to Malicka-Kleparska's analysis, the stress pattern of -al nouns is not a condition on the use of the suffix, but only a predictable result of the morphological structure of the verbs that it attaches to (p. 437).