A lilu or lilû is a masculine Akkadian word for a spirit, related to Alû, demon.
The wicked Utukku who slays man alive on the plain.
The wicked Alû who covers (man) like a garment.
The wicked Etimmu, the wicked Gallû, who bind the body.
The Lamme (Lamashtu), the Lammea (Labasu), who cause disease in the body.
The Lilû who wanders in the plain.
They have come nigh unto a suffering man on the outside.
They have brought about a painful malady in his body.
Dating of specific Akkadian, Sumerian and Babylonian texts mentioning lilu (masculine), lilitu (female) and lili (female) are haphazard. In older out-of-copyright sources, such as R. Campbell Thompson's The Devils and Evil Spirits of Babylonia (1904) specific text references are rarely given. An exception is K156 which mentions an ardat lili Jo Ann Scurlock and Burton R. Andersen (2005) see the origin of lilu in treatment of mental illness.
The Assyriologist Heinrich Zimmern who produced a study of all the words in the Hebrew Bible which could be related or derived from Akkadian (1917) tentatively identified vardat lilitu KAT3, 459 as paramour of lilu. 
Possible Jewish associations
It is disputed whether, if at all, the Akkadian word lilu, or cognates, is related to the disputed Hebrew word liyliyth in Isaiah 34:14, which is thought to be a night bird by some modern scholars such as Judit M. Blair. The Babylonian concept of lilu may be more strongly related to the later Talmudic concept of Lilith (female) and lilin (female).
- Deliver Me from Evil: Mesopotamian Incantations, 2500-1500 BC - Page 149 Graham Cunningham - 1997 "Partly or wholly bilingual incantations in the Old Babylonian period (continued)
Text 313: Geller 1989 text An, Malluhi, Directed against witchcraft PBS 1/2 122 b Enki, Utu Features divine dialogue" (partly bilingual)
- Deliver Me from Evil: Mesopotamian Incantations, 2500-1500 BC - Page 177 Graham Cunningham - 1997 "This is particularly the case in Sumerian incantations, with only two of the daimons specified in Sumerian texts being mentioned in Akkadian incantations, Lamastu and to a lesser degree Ardat Lili. In contrast to the Sumerian attribution "
- Major-General Sir H. C. Rawlinson. Cuneiform Inscriptions of Western Asia. Vol. 4 (Semitic). ed. Theophilus Pinches. London: British Museum, 1861–64, 1891.
- Thompson p.XXXVIII
- Diagnoses in Assyrian and Babylonian medicine: ancient sources 2005 Page 435 "The reason for the attribution of this disorder to the lilu was probably that the majority of patients developed characteristic symptoms in adolescence or early adulthood. This pattern of onset is characteristic of some mental disorders"
- Akkadische Fremdwörter als Beweis für babylonischen Kultureinfluß. Leipzig, 1917
- Aramaic Incantation Texts from Nippur - Page 76 James Alan Montgomery - 2011 "So in the Talmud they dwell in the beams and crevices, the cesspools, etc.,52 even as in Greek magic demons 45 Acc. to Zimmern, KAT3, 459 = paramour of lilu. Better Thompson. (Devils, etc., i, p. xxxvii, Semitic Magic, 65), who regards the ..."
- Blair J. M. De-demonising the Old Testament: An Investigation of Azazel