Verbseoul.
하다 verb (adj)
고약하다goyakhadaawful, nasty, foul

To say awful, nasty, foul politely in the present tense, use 고약해요 (goh-yah-kae-yoh). Below is the full conjugation of 고약하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
고약해
goh-yah-kae
고약해요
goh-yah-kae-yoh
고약합니다
goh-yah-kahm-nee-dah
Past
고약했어
goh-yah-kae-ssuh
고약했어요
goh-yah-kae-ssuh-yoh
고약했습니다
goh-yah-kae-sseum-nee-dah
Future
고약할 거야
goh-yah-kahl- -guh-yah
고약할 거예요
goh-yah-kahl- -guh-yae-yoh
고약할 겁니다
goh-yah-kahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
고약하세요
goh-yah-kah-sae-yoh
Suggestion / Let's Polite (요)
고약해요
goh-yah-kae-yoh
Question Polite (요)
고약해요?
goh-yah-kae-yoh-?
Connective “and” — (고)
고약하고
goh-yah-kah-goh
Conditional “if” — (면)
고약하면
goh-yah-kah-myuhn
Noun form — (기)
고약함
goh-yah-kahm