Verbseoul.
하다 verb (adj)
둔하다dunhadato be dull, slow, inert, obtuse, dim-witted

To say to be dull, slow, inert, obtuse, dim-witted politely in the present tense, use 둔해요 (doon-hae-yoh). Below is the full conjugation of 둔하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
둔해
doon-hae
둔해요
doon-hae-yoh
둔합니다
doon-hahm-nee-dah
Past
둔했어
doon-hae-ssuh
둔했어요
doon-hae-ssuh-yoh
둔했습니다
doon-hae-sseum-nee-dah
Future
둔할 거야
doon-hahl- -guh-yah
둔할 거예요
doon-hahl- -guh-yae-yoh
둔할 겁니다
doon-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
둔하세요
doon-hah-sae-yoh
Suggestion / Let's Polite (요)
둔해요
doon-hae-yoh
Question Polite (요)
둔해요?
doon-hae-yoh-?
Connective “and” — (고)
둔하고
doon-hah-goh
Conditional “if” — (면)
둔하면
doon-hah-myuhn
Noun form — (기)
둔함
doon-hahm