diff --git a/src/core/dictionary.rs b/src/core/dictionary.rs
index 9ec5093..8ad6e58 100644
--- a/src/core/dictionary.rs
+++ b/src/core/dictionary.rs
@@ -165,6 +165,10 @@ impl Dictionary {
         }
         define_word_impl(&mut self.words, name.into(), word, allow_redefine)
     }
+
+    pub fn undefine_word(&mut self, name: &str) -> bool {
+        self.words.remove(name).is_some()
+    }
 }
 
 type WordsMap = HashMap<String, DictionaryEntry>;
diff --git a/src/core/mod.rs b/src/core/mod.rs
index 16d0478..e1dd694 100644
--- a/src/core/mod.rs
+++ b/src/core/mod.rs
@@ -26,6 +26,8 @@ pub struct Context<'a> {
     pub dictionary: Dictionary,
 
     pub input: Lexer<'a>,
+    pub clock: &'a dyn Clock,
+
     pub stdout: &'a mut dyn Write,
 }
 
@@ -38,6 +40,7 @@ impl<'a> Context<'a> {
             next: None,
             dictionary: Default::default(),
             input: Lexer::new(input),
+            clock: &SystemClock,
             stdout,
         }
     }
@@ -51,6 +54,15 @@ impl<'a> Context<'a> {
         module.init(&mut self.dictionary)
     }
 
+    pub fn with_clock(mut self, clock: &'a dyn Clock) -> Self {
+        self.set_clock(clock);
+        self
+    }
+
+    pub fn set_clock(&mut self, clock: &'a dyn Clock) {
+        self.clock = clock;
+    }
+
     pub fn run(&mut self) -> Result<u8> {
         let mut current = Some(Rc::new(InterpreterCont) as Cont);
         while let Some(cont) = current.take() {
@@ -166,6 +178,21 @@ impl<T: Module> Module for &T {
     }
 }
 
+pub trait Clock {
+    fn now_ms(&self) -> u64;
+}
+
+struct SystemClock;
+
+impl Clock for SystemClock {
+    fn now_ms(&self) -> u64 {
+        std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap()
+            .as_millis() as u64
+    }
+}
+
 struct InterpreterCont;
 
 impl ContImpl for InterpreterCont {
diff --git a/src/core/stack.rs b/src/core/stack.rs
index b2db8f6..fe652d3 100644
--- a/src/core/stack.rs
+++ b/src/core/stack.rs
@@ -69,11 +69,11 @@ impl Stack {
     }
 
     pub fn push_bool(&mut self, value: bool) -> Result<()> {
-        self.push(BigInt::from(if value {
+        self.push(if value {
             -BigInt::one()
         } else {
             BigInt::zero()
-        }))
+        })
     }
 
     pub fn push_int<T: Into<BigInt>>(&mut self, value: T) -> Result<()> {
diff --git a/src/modules/control.rs b/src/modules/control.rs
index 73386a1..bf951d8 100644
--- a/src/modules/control.rs
+++ b/src/modules/control.rs
@@ -219,6 +219,27 @@ impl Control {
         ctx.stack.push_argcount(0, ctx.dictionary.make_nop())
     }
 
+    #[cmd(name = "forget", args(word_from_stack = false))]
+    #[cmd(name = "(forget)", args(word_from_stack = true))]
+    fn interpret_forget(ctx: &mut Context, word_from_stack: bool) -> Result<()> {
+        let mut word = if word_from_stack {
+            *ctx.stack.pop_string()?
+        } else {
+            let word = ctx.input.scan_word()?.ok_or(Error::UnexpectedEof)?;
+            word.data.to_owned()
+        };
+
+        if ctx.dictionary.lookup(&word).is_none() {
+            word.push(' ');
+            if ctx.dictionary.lookup(&word).is_none() {
+                return Err(Error::UndefinedWord);
+            }
+        }
+
+        ctx.dictionary.undefine_word(&word);
+        Ok(())
+    }
+
     // === Input parse ===
 
     #[cmd(name = "word")]
diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index 363b033..2409bf1 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -123,4 +123,14 @@ impl FiftModule for BaseModule {
 
         Ok(())
     }
+
+    #[cmd(name = "now")]
+    fn interpret_now(ctx: &mut Context) -> Result<()> {
+        ctx.stack.push_int(ctx.clock.now_ms() / 1000)
+    }
+
+    #[cmd(name = "now_ms")]
+    fn interpret_now_ms(ctx: &mut Context) -> Result<()> {
+        ctx.stack.push_int(ctx.clock.now_ms())
+    }
 }