One of the key things about bible study is my often repeated adage that 'bible words do not have definitions they have histories'. This is particularly important with words relating to 'repentance'. Much of the vocabulary of the Greek New Testament has an Old Testament Hebrew mind-set root. The Greek word metanoia, for example, cannot be understood alone by reference to Classical or even contemporary Greek. The LXX had provided a Greek vocabulary for many Hebrew words which means that when we encounter them in the New Testament they already have a hidden history.
An example of this might be 'ekklesia' which is usually translated 'church' in our English versions. 'ekklesia' is a Greek word but it had been used to translate a Hebrew concept. qahal is used in over a hundred verses in the OT
Gen. 28:3; 35:11; 48:4; 49:6; Ex. 12:6; 16:3; Lev. 4:13-14,21; 16:17,33; Num. 10:7; 14:5; 15:15; 16:3,33,47; 19:20; 20:4,6,10,12; 22:4; Deut. 5:22; 9:10; 10:4; 18:16; 23:1-3,8; 31:30; Josh. 8:35; Judg. 20:2; 21:5,8; 1Sam. 17:47; 1Kings 8:14,22,55,65; 12:3; 1Chr. 13:2,4; 28:8; 29:1,10,20; 2Chr. 1:3,5; 6:3,12-13; 7:8; 20:5,14; 23:3; 24:6; 28:14; 29:23,28,31-32; 30:2,4,13,17,23-25; 31:18; Ezra 2:64; 10:1,8,12,14; Neh. 5:13; 7:66; 8:2,17; 13:1; Job 30:28; Psa. 22:22,25; 26:5; 35:18; 40:9-10; 89:5; 107:32; 149:1; Prov. 5:14; 21:16; 26:26; Jer. 26:17; 31:8; 44:15; 50:9; Lam. 1:10; Ezek. 16:40; 17:17; 23:24,46-47; 26:7; 27:27,34; 32:3,22-23; 38:4,7,13,15; Joel 2:16; Mic. 2:5
In over 70 of these instances the LXX translated qahal by the Greek word 'ekklesia'. When Christ said 'I will build my church' the disciples already knew the conceptual meaning of the word. All they had to do was to transpose it into their new setting.
We are probably most familiar with its use in Psalm 22 where it is translated as 'congregation' in the KJV. Psa. 22:22 I will declare thy name unto my brethren: in the midst of the congregation will I praise thee.
Psa. 22:25 My praise shall be of thee in the great congregation: I will pay my vows before them that fear him. We are probably also aware that when Psalm 22 is quoted in the letter to the Hebrews the KJV uses the word 'church' from its underlying Greek word 'ekklesia'.
For this reason you are absolutely right to go back into the Hebrew and to pick out the sense of 'grief' that is to be found in the Hebrew concept. The point is that we must then add that to all NT uses of 'metanoia' because, as with all languages, use has redefined the word. Those who say that 'metanoia' only means a 'change of mind' have completely missed this vital ingredient of word study as pertaining to the scriptures. Consequently 'metanoia' in the New Testament must be understood as the Hebrew mind-set would understand it and not restrict itself to the specific word definition as would be found in a Greek lexicon.