The verb "suit" is part of the defective verbs, which are characterized by no possess all the inflections. They are only conjugated in arrhizotonic forms, that is, in forms in which the tonic accent occurs outside the root.
Let's see: the stressed syllable of the verb “adequate” is “quar”, so the forms in which the accent falls on the previous syllable “de” cannot be used. This is the case of the prayers “I am not suitable for this type of assessment” or even “I am not suitable for this type of assessment”. In the latter case in which the accent falls on "qu", the use is also wrong, since the verb is used in the forms in which the accent appears after the "qu", as in: adewhatThemos, adewhatTheof.
This verb is conjugated in the present tense only in the 1st and 2nd person plural, in the second person plural of the imperative (adequai), not having inflections in the present tense of the subjunctive. As for the other forms, it remains within the usual standards.
This also occurs with other verbs, such as: abolish, banish, color, demolish, stink, bark.
These verbs are not conjugated in all verb forms for a number of reasons. Some because they would cause mistakes with conjugations of other verbs, others because of euphony or pejorative use and others more because they are not usual in the language.
We observe the verb “adequate” most often conjugated in the infinitive mode (adequate) and in the participle (adequate). However, as explained above, this verb is frequently used in other tenses, moods and persons, such as: adequa, adeqúo, adeqúa.
As much as the verb "adequate" may come to be accepted by grammarians, due to its habitual use, it is better that for the time being replaced by synonyms or accompanied by an assistant: adapt, accommodate, adjust, I want to adapt, I try to adapt, be adequate.
By Sabrina Vilarinho
Graduated in Letters
Brazil School Team
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Source: Brazil School - https://brasilescola.uol.com.br/gramatica/adequo-ou-adequo.htm