Why is the ninth month called September?
Old English murnan "to mourn, bemoan, long after," also "be anxious about, be careful" (class III strong verb; past tense mearn, past participle murnen), from Proto-Germanic *murnan "to remember sorrowfully" (cf. Old Saxon mornon, Old High German mornen, Gothic maurnan "to mourn," Old Norse morna "to pine away"), probably from PIE root *(s)mer- "to remember" (see memory); or, if the Old Norse sense is the base one, from *mer- "to die, wither." Related: Mourned; mourning.
Frequent references are found in Scripture to, (1.) Mourning for the dead. Abraham mourned for Sarah (Gen. 23:2); Jacob for Joseph (37:34, 35); the Egyptians for Jacob (50:3-10); Israel for Aaron (Num. 20:29), for Moses (Deut. 34:8), and for Samuel (1 Sam. 25:1); David for Abner (2 Sam. 3:31, 35); Mary and Martha for Lazarus (John 11); devout men for Stephen (Acts 8:2), etc. (2.) For calamities, Job (1:20, 21; 2:8); Israel (Ex. 33:4); the Ninevites (Jonah 3:5); Israel, when defeated by Benjamin (Judg. 20:26), etc. (3.) Penitential mourning, by the Israelites on the day of atonement (Lev. 23:27; Acts 27:9); under Samuel's ministry (1 Sam. 7:6); predicted in Zechariah (Zech. 12:10, 11); in many of the psalms (51, etc.). Mourning was expressed, (1) by weeping (Gen. 35:8, marg.; Luke 7:38, etc.); (2) by loud lamentation (Ruth 1:9; 1 Sam. 6:19; 2 Sam. 3:31); (3) by the disfigurement of the person, as rending the clothes (Gen. 37:29, 34; Matt. 26:65), wearing sackcloth (Gen. 37:34; Ps. 35:13), sprinkling dust or ashes on the person (2 Sam. 13:19; Jer. 6:26; Job 2:12), shaving the head and plucking out the hair of the head or beard (Lev. 10:6; Job 1:20), neglect of the person or the removal of ornaments (Ex. 33:4; Deut. 21:12, 13; 2 Sam. 14:2; 19:24; Matt. 6:16, 17), fasting (2 Sam. 1:12), covering the upper lip (Lev. 13:45; Micah 3:7), cutting the flesh (Jer. 16:6, 7), and sitting in silence (Judg. 20:26; 2 Sam. 12:16; 13:31; Job 1:20). In the later times we find a class of mourners who could be hired to give by their loud lamentation the external tokens of sorrow (2 Chr. 35:25; Jer. 9:17; Matt. 9:23). The period of mourning for the dead varied. For Jacob it was seventy days (Gen. 50:3); for Aaron (Num. 20:29) and Moses (Deut. 34:8) thirty days; and for Saul only seven days (1 Sam. 31:13). In 2 Sam. 3:31-35, we have a description of the great mourning for the death of Abner.
formal demonstration of grief at the death of a person, practiced in most societies. Mourners are usually relatives, although they may be friends or members of the community. Mourning rites, which are of varying duration and rationale, usually weigh more heavily on women than on men. Mourners may deny themselves certain amusement, ornaments, or food. They may practice sexual continence or keep vigil over the body of the deceased. Changes in garb, such as black robes, and alterations in hairstyle may distinguish mourners, but such evidences of mourning have declined in many societies.