Verbseoul.
하다 verb (adj)
튼튼하다teunteunhadasturdy, strong

To say sturdy, strong politely in the present tense, use 튼튼해요 (teun-teun-hae-yoh). Below is the full conjugation of 튼튼하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
튼튼해
teun-teun-hae
튼튼해요
teun-teun-hae-yoh
튼튼합니다
teun-teun-hahm-nee-dah
Past
튼튼했어
teun-teun-hae-ssuh
튼튼했어요
teun-teun-hae-ssuh-yoh
튼튼했습니다
teun-teun-hae-sseum-nee-dah
Future
튼튼할 거야
teun-teun-hahl- -guh-yah
튼튼할 거예요
teun-teun-hahl- -guh-yae-yoh
튼튼할 겁니다
teun-teun-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
튼튼하세요
teun-teun-hah-sae-yoh
Suggestion / Let's Polite (요)
튼튼해요
teun-teun-hae-yoh
Question Polite (요)
튼튼해요?
teun-teun-hae-yoh-?
Connective “and” — (고)
튼튼하고
teun-teun-hah-goh
Conditional “if” — (면)
튼튼하면
teun-teun-hah-myuhn
Noun form — (기)
튼튼함
teun-teun-hahm