by (formerly also †upon) my truth: expressing strong affirmation or assertion. Cf. by my troth at troth, n. adv.phrases 2. Now archaic and rare.

in faith, i'faith y'faith: in truth, really, truly. Frequently used parenthetically as an oath or to emphasize the truth of a statement. Cf…

Used interjectionally.

Expressing assent; cf. true, adj. 4b. Also as an intensifier: = in truth at phrases 1c. Also as int. Cf. troth, adv. Obsolete (archaic and poetic…

Emphasizing the truth or honesty of a statement or assertion; ‘in truth’, ‘truly’. Cf. earlier in good faith at phrases a, faith, int. Now rare.

In truth, truly; in fact, indeed. Also as int. Cf. truth, adv. Now rare.

‘Is it not so?’ Used esp. to emphasize the truth or probability of the preceding statement.

In interrogative contexts (esp. amongst German-speakers): ‘Is it not true?’; ‘Isn't that so?’ Cf. n'est-ce pas, phr.

The adjective used absol. (quasi-n.) in certain phrases. the straight: the truth. Esp. in to get (at) or hear the straight. U.S.

Frequently used interrogatively as an int. (cf. indeed, adv. 6, and equivalent foreign expressions n'est-ce pas, phr., nicht wahr, phr.).