Google definition (this method is frowned upon by Google, use for educational purposes only).

define

#!/usr/bin/env ruby
# Define: a Google Dictionary API tool

require "rubygems"
require "net/http"
require "json"

if not ARGV[0]; exit; end

query 	 = ARGV.join("+").gsub(" ","+")
response = Net::HTTP.start("www.google.com",80) do |http|
	   http.get("/dictionary/json?callback=r&sl=en&tl=en&q="+query); end

begin
	data	 = JSON.parse(/r\((:?.*?),200,null\)/.match(response.body)[1])
	phonetic = data["primaries"][0]["terms"][1]["text"]
	label	 = data["primaries"][0]["terms"][0]["labels"]
	type	 = (label)?label[0]["text"]:"person"
	puts	   "\n%s %s (%s)\n" % [data["query"].capitalize, phonetic, type.downcase]

	for i in (0..5)
		entry = data["primaries"][0]["entries"][i]["terms"][0]["text"].
		gsub(/(x3cemx3e|x3c\/emx3e)/,"").scan(/.{1,80}(?:\s|\Z)/)
		puts "\u2022 "+entry[0].capitalize
		entry[1..-1].each do |line|; puts "  "+line; end
	end
	puts
rescue	
	puts
	exit
end