Whilst the earlier posts seem to show a traditional style of knife perhaps used by the Mahout etc ...The later form which are sickle like are originally south Indian and used also in Sri Lanka . They are Veecharuval.
See THE Veecharuval on
http://www.vikingsword.com/vb/showth...&page=11&pp=30 at post#304... This weapon may have spread from Southern India moreover there it is banned in many areas since it has been used in frequent attacks and murders... It is simply a machete often with a curved hook like tip section...The use of agricultural tools as war or fighting weapons is not unusual and this is an example of such an item. For interest I show the South Indian version in the blacksmiths shop though there is, perhaps, little difference.