def rand_btw(low,high)
  srand(Time.now.to_i)
  loop do
    t = rand(high)
    return t if t > low
  end
end

srand(Time.now.to_i)
word_size = rand_btw(6,15)
ascii_set = []
word = ""
i = 0
loop do
  num = rand_btw(97,122)
  if ascii_set.include?(num) then next else ascii_set << num end
  word << num.chr
  break if i > word_size
  i += 1
end

p word