hook_options_list not getting fired in a custom module I need to limit taxonomy term reference field options based on another field.This is needed as there are around 1000 terms available for this 'Select' field but I want to limit these options to a minimum using hook_options_list. 

But this hook is not getting called from the custom module, not much detail provided on the drupal help too. 

Does this hook require any prerequisite so it can be called.
You can use hook_field_info_alter() to attach custom allowed_values_function to your field and implement your own logic there:

function my_module_field_info_alter(&amp;$info) {
  $info['my_field']['settings']['allowed_values_function'] = 'my_module_my_field_allowed_values_callback';
}

function my_module_my_field_allowed_values_callback($field, $instance, $entity_type, $entity) {
  // Custom logic
  return $values;
}