In any language a word can have different meanings.
Let's look at the PTS's dictionary definition:
Pali Text Society wrote:Sangha [fr. saŋ+hṛ; lit. "comprising." The quâsi pop. etym. at VvA 233 is "diṭṭhi -- sīla -- sāmaññena sanghāṭabhāvena sangha"] 1. multitude, assemblage Miln 403 (kāka˚); J i.52 (sakuṇa˚); Sn 589 (ñāti˚); 680 (deva˚); D iii.23 (miga˚); Vv 55 (accharā˚=samūha VvA 37). bhikkhu˚ an assembly of Buddhist priests A i.56, etc.; D i.1, etc.; S i.236; Sum i.230, 280; Vin i.16; ii.147; bhikkhunī˚ an assembly of nuns S v.360; Vin i.140; sāvaka˚ an assembly of disciples A i.208; D ii.93; S i.220; PvA 195, etc.; samaṇa˚ an assembly of ascetics Sn 550. -- 2. the Order, the priesthood, the clergy, the Buddhist church A i.68, 123, etc.; D i.2, etc.; iii.102, 126, 193, 246; S iv.270 sq.; Sn 227, etc.; J ii.147, etc.; Dhs 1004; It 11, 12, 88; Vin i.102, 326; ii.164, etc. <-> 3. a larger assemblage, a community A ii.55=Sv.400; M i.231 (cp. gaṇa). -- On the formula Buddha, Dhamma, Sangha see dhamma C 2.
- http://dsal.uchicago.edu/cgi-bin/philol ... :2839.pali
So a Sangha could be a group of ordained Monks, Nuns, or it could be a large lay community.
If you got a bunch of lay people together and called yourself a Sangha you might recieve some politely worded letters though